A rare and eerie weather phenomenon shocked beachgoers in Portugal on Sunday, as a massive cloud resembling a tsunami swept across the sky — and quickly went viral online.

In the video, which has been widely shared on social media, the cloud appears as a giant wall, creating the illusion that it’s about to crash down onto the beach like an enormous wave.

Cloud Tsunami Sweeps Over Three Portuguese Cities

A rare atmospheric phenomenon rolled across Portugal — a giant “roll cloud” resembling a tsunami in the sky. It was spotted in three coastal cities.

These clouds form due to sea breezes and appear as a long, horizontal mass… pic.twitter.com/H3KQeXB58p

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According to international media outlets, this mesmerizing scene was caused by a rare meteorological event known as a roll cloud.

These clouds form due to the interaction of air masses with contrasting temperatures, often combined with sea breezes. The result is a tubular-shaped cloud that rolls horizontally across the sky — mimicking the appearance of a giant ocean wave, though it is not related to tsunamis.

As the cloud formation approached the coastline, strong winds suddenly struck the beaches, catching swimmers and sunbathers by surprise.